Belongs to the Order Rhizostomae, Family
Cepheidae. One of the most common jellyfish in the Mediterranean sea
and definitely the most colorful of all. Usually they are found in
great numbers in the Aegean and the Adriatic sea. The animal can
grow to 35 cm in diameter (the animal shown in the following series
of pictures is a fully grown adult) and in contrast to most
jellyfishes has an ability to move on its own (does not necessarily
follow water currents). In the sea it is a magnificent animal. It
migrates vertically while various juvenile fishes are associated
with it. In the photos shown, the fishes which live around and in it
are juvenile Seriola dumerili.

C. tuberculata has separate sexes and the eggs
are fertilized internally, the larvae kept in pockets and then are
released in the open water where they developed into sessile polyps.

This species is not recommended for aquaria for
two reasons: First, it feeds on microplankton and second they need
an extremely wide aquarium in order to avoid hitting the aquarium
glass which will damage it. Stay assured that if I could keep it, I
would. The way it majestically moved in the water coupled to the
colorful and unique appearance would make a nice addition to any
Mediterranean tank.

Morphologically it is characterized by a
flattened region along its margin and has a dome at the center of
its umbrella giving it the appearance of a large fried egg when
viewed of above (see photos below). There are many, variable-length
tentacles attached to eight lappets. It has eight oral arms which
are brittle, short and fused proximally. Numerous blue or purple
tipped appendages are located between each of the oral arms. These
colors are due to the presence of unicellular symbiotic algae (zooxanthelle).

It is found in aggregations in the open water
of the high seas and along coastlines.

Photos taken in Aegean Sea (Saronic gulf) in
September 2003.

New
In March 2004, the following question was sent to MCH by James
White, London, UK:

I was swimming in the
Mar Menor and found myself surrounded by hundreds of what I now know
to be cotylorhiza tuberculata, (thanks to your web site). I would be
interested if you have any information about the seriousness of
their sting.

Dr.
Peter Nicolaides

Are we talking
about the jelly-fish which is round, darkish-yellow-brown, fried-egg
appearance on top (smooth round bump on top) with short tentacles
(compact, no tentacles dangling/trailing) with a small flat whitish
disc on each end, with (usually) a small school of fish darting with
impunity in and out of that cluster? If it is this one, the sting is
very mild in my experience and does not leave any skin lesions.
However, venom strength may vary. The size of these rather
impressive creatures can range from ~8-10 cm diameter to 30 or even
50 ! The best reference book available (maybe in libraries, 'cos it
is quite expensive) is a two-volume monster by Halstead "Poisonous
and Venomous Animals of the Sea". Last time I saw that was in the
Natural History Museum in London.

If I remember
well, the venom is quite complex so the only action that may relieve
pain is to apply hot-water compresses (as hot as you can bear,
~45-47 C) and that should start denaturing the proteins of the
venom.

Dr. Alexandros
Frantzis

As far as I know
Cotylorhiza tuberculata is not dangerous for human beings. I have
touched or held them with naked hands many times. To give you an
idea, once a colleague of mine put one of them on the top of his
head as a hat(!!!) to show that it was not dangerous...
Nevertheless, all jellyfish have toxins and acids that can be
dangerous to a varying degree depending on where and how they can
reach the human body. For example some species (like Pelagia
noctiluca) are harmless if you just touch them with the "ventral"
part of your fingers, but if a tentacle reaches the "dorsal" part of
your hand or if just after touching it you touch your face, believe
me you will have problems! Another issue is the degree of
sensitivity that also varies a lot from one person to another, so I
cannot completely exclude that for a very sensitive skin even
Cotylorhiza could be a problem...